We propose to study 2 groups of patients to determine the significance of leukoencephalopathy on MRI. Group 1 are patients on MRI who have lesions. Group 2 are controls. All patients will undergo neurological and neuropsychological evaluation as out-patients on the CRC. Those with dementia and leukoencephalopathy will be admitted for cisternography. The extent of the white matter involvement will be correlated with clinical state and neuropsychological testing.